Here's a statement from Terrence in this thread:

http://www.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=001067#000005

'One of the issues with DCPs is there is no Mono option. It's stereo, then additional channels in even increments. So really, you'd go from stereo to 5.1, then 7.1 and so on. If you wanted mono, you'd need to create a 5.1 DCP with silence tracks on everything but the center. Kind of a pain.'

- Carsten